Method op



Reissued Apr. 7, 1931 PATENT OFFICE JONAS HJ'ALMAR MELLQUIST, OF STOCKEOLM, SWEDEN METHOD OF APPLYING PROTECTIVE LAYERS ON METALS OR OTHER ELECTRIC CONDUCTORS No Drawing. Original No. 1,595,675, dated August 10, 1926, Serial No. 729,656, filed August 1, 1;]24, and in Sweden August 23, 1923. Application for reissue filed July 24, 1930. Serial No. 470,547.

It is known that iron is rendered passive by being used as an anode in an alkaline Solution and that this quality is highly increased by precipitating on the iron a layer of high oxidation potential, such as' lead peroxide. Attempts have been made to util ize this condition for technical purposes in order to protect the iron against rusting.

If a solution of, for instance, lead nitrate be electrolyzed, there is formed on the anode a layer of lead peroxide, but after a relatively short period such a bath will be acidified by the liberated nitric acid which attacks the objects used as the anode and is gradually reduced to nitrous acid so that finally no further precipitation of peroxide occurs.

By using as an electrolyte a solution obtained by boiling lead oxide in a concentrated alkali solution great inconveniences soon occur which makethe process inapplicable for technical use, such inconveniences principally consisting in this that the tension will be exposed to strong variations, an evolution of gases occurs and a slimy mixture of hydrates of lead of different stages of oxidation is formed.

It has now been discovered that such layers of a high oxidation potential may be precipitated on the anodes very easily without any disturbing actions or variations of the tensions by'using as an electrolyte an alkaline solution 'of a lead, manganese or other metal salt of a hydroxy carboxylic acid, which metal is adapted to form peroxides. Amongst such acids the tartaric acid is preferred due to its relatively low price.

The present invention therefore has for its object to provide an electrogalvanic method of applying protective layers to electric conductors, especially metals, which consists in using said conductors as an anodein an alkaline solution, including ammoniacal solution, of a hydroxy carboxylic acid salt of a metal adapted to form peroxide. The preferred salts used in carrying'the invention into practice are lead or manganese salts of hydroxy carboxylic acids, es ecially of tartaric acid, but also such salts 0? other metals adapted to form peroxides may be used such as nickel,

cobalt, bismuth.

The bath to be electrolyzed may be prepared as follows:

A solution of a lead salt, such as lead acetat-e or nitrate, is added with a solution of a tartrate of an alkali metal, such as sodiumpotasslnm tartrate. The precipitation thus formed, which in a dry stateis a white line crystalline powder, corresponding to the emp1r1c formula PbC H O is Washed by re peated decantations and is finally suspended in water, whereupon a solution of about 10% of an alkali such as NaOH or ammonia is added in slight excess until a clear solution is formed. A complex alkalilead compound of tartaric acid is thereby formed.

Another method of obtaining such a solution which can be more easily executed consists in shaking a solution of a tartrate of an alkali metal to which has been added a suitable quantity of finely pulverized lead oxide or lead hydrate. If for instance a solution containing grams of sodium-potassium tartrate per' litre is shaken together with a suitable quantity of finely pulverized lead oxide an alkaline solution is obtained which contains about 30 grams of lead in solution per litre. The dissolving takes place more rapidly if at the beginning an alkali is added and the mixture heated. The obtaining of a corresponding solution of manganese ismore difiicult, and, moreover, such a solution has tendency of being oxidized by the air.

For technical purposes the bath may be produced in the following manner, the quantities of the ingredients as well as the method itself being only given as examples:

Example I 150 grams of pure sodium hydrate are dissolved in 10 litres of distilled Water, whereupon after stirring 450 grams of potassium bitartrate are added. WVhen this salt has been dissolved 400500 grams of finely pulverized lead oxide are added and the mixture stirred. Together with said oxide one i may add manganese oxide or manganese hydrate. The mixture .is then vigorously stirred from time to time while being heated, if desired, .until most of the lead has dissolved. After the undissolved residue has settled to the Example I I The bath may be composed as follows:

10 litres of water, 500 grams of sodiumpotassium tartrate, 50-100 grams of sodum: hydrate, 400-500 grams of finely pulverized lead oxide.

On executing the method one may use as a cathode plates of iron or other suitable metal of convenient shape and size and as an anode the objects on which the protective layer is to be precipitated. The objects used as the anode are freed from fat and carefully purified in any convenient manner before being placed into the bath. If the anode consists of iron it may be conveniently treated with a 10% solution of nitric acid and the remaining carbon may be removed by brushing or in any other convenient manner. The objects may also be purified by subjecting them to the action of sand blast in Which case the surface will be more smooth than by using chemical agents. Generally the result will be best. if the anode-objects are made dull in some way or other.

lVhen the layer has receivedthe desired thickness the objects are rapidly removed from the bath, flushed with a stream of water which should first be cold and then hot, and finally they are dried. By suitably adapting the length of the period during which the objects are exposed to the galvanic action a perfectly even and rigidly adhering layer.

or cover is obtained on'the objects used as the anode. Said layer has a dark-blue or dark-gray colour and consists of hydratic peroxide of lead or manganese.

The above described method which is well adapted for working one technical scale makes it possible to apply on objects of iron or other metals or other electric conductors,

' such as carbon, a protective layer or cover which will protect the objects against the corrosive action of the atmosphere. of acids, gases and other agents. Objects of iron, for instance, will in this manner be protected against rusting. The layer or cover thus obtained will obtain a deep black colour if the 3. Electrogalvanic method of applying protective covers on electric conductors, es-

pecially metals. consisting in using said conductors as anode in an alkaline solution of a lead salt of tartaric acid.

4. Electrolytic bath adapted to be used in executing the method set forth in claim 2,

consisting of a solution of a lead compound in an alkali tartrate solution.

5. Electrolytic bat-h adapted to be used in executing the method set forth in claim 2,

' consisting of a solution of a lead compound in alkali tartrate solution to which has been added an alkali.

6. Electrolytic bath adapted to be used in executing the method set forth in claim 2, I

consisting of a solution of a mixture of a lead compound and a manganese compound in an alkali tartrate solution.

In testimony whereof I have aflixed my signature.

JONAS HJALMAR MELLQUIST.

objects are providedwith a cover of pyroxy-y n line varnish or dipped into a solution of parafiin, wax or similar substances. For obtaining covers of greater thickness, for instance on objects adapted to be used as or in connection with electrodes a considerably 7 longer period is of course required than in case of producing a cover protecting against rust.

Whenever the process is interrupted, for instance at the end of a day the undissolved lead oxide on the bottom of the vessel is stirred in the liquid until the latter contains the original amount of lead in solution.- Fresh oxide of lead is introduced into the liquid 

